With the rapid development of wireless communication technology, wireless terminals (mobile phone, data card, MiFi/Hotspot product) have been applied more and more widely. At the same time, the influence of electromagnetic radiation on human bodies brought about by the wireless terminal has become a public concern.
Most existing SAR reducing techniques adopt a method such as reduction of transmitter power, use of wave absorbing material or of a conductor reflector and shield, and radiation-proof and wave-absorbing coating on a casing surface, etc., which will not only increase costs and process complexity, but also affect a communication signal, thereby failing to fundamentally solve the contradiction between human body radiation safety and high-quality wireless communication. In addition, more space is required for the location of the reflector and shield during assembly, which is contrary to the purpose of miniaturized design of the wireless terminal.
Additionally, a mechanism of forming a local SAR peak value is the joint contribution from the surface current of an antenna conductor per se and the surface current induced on metal surfaces in the antenna near field, such as a Printed Circuit Board (PCB) metal ground, a shielding cover, and a shielding frame. In a wireless terminal device, the exposed circuit shielding cover, PCB substrate metal ground, housing, and the antenna would interact with each other to form a complicated boundary condition. The SAR peak value generally appears near a maximum local current at the antenna or a PCB metal surface. Currently, the parasitic conductor structures such as a PCB grooving or a conductive ring structure are usually added near the antenna or on the PCB to alter the surface current distribution, so as to reduce an SAR value. However, such technique takes up much more space, and is applicable to one-directional SAR reduction for a product such as the mobile phone, but not applicable to a data card wireless terminal product.